Doherty amplifiers are amplifiers commonly used in wireless communication systems. Doherty amplifiers are used in base stations that enable the operation of wireless communications networks. Doherty amplifiers are suitable for use in such applications because the amplifiers include separate amplification paths, e.g., a carrier path and a peaking path. Amplifiers in the two paths are configured for operation at different classes. An amplifier in a carrier (or main) path is biased for operation in a class AB mode. An amplifier in a peaking amplification path operates in a class C mode.
The combination of the amplification paths and different modes of operation leads to improved power-added efficiency and linearity relative to, for instance, a balanced amplifier, at the power levels commonly encountered in wireless communications applications. When the carrier amplifier is operating below compression, the peaking amplifier is not operating. The linearity and efficiency of the carrier amplifier are thus not adversely affected by the peaking amplifier. Once the input power levels place the carrier amplifier into compression, the peaking amplifier begins to operate to thereby supplement the output of the carrier amplifier to maintain linearity. The Doherty amplifier thus provides efficient and linear operation over a wide range of input power levels.
A power splitter supplies the input signals to each amplification path in a Doherty amplifier. The power splitter divides the input signal into two or more signals in accordance with the architecture of the Doherty amplifier. The power splitter also adjusts the phase of the input signal for one or more of the amplification paths in accordance with the architecture, or type, of Doherty amplifier.
Doherty amplifiers are available in a number of different architectures. Examples include various types of two-way, three-way, or N-way Doherty amplifiers in accordance with the number of peaking amplification paths. Each Doherty amplifier may be configured as a conventional or inverted Doherty amplifier. Other differences in Doherty architectures involve symmetries or asymmetries in the size of the carrier and peaking amplifiers.
Different Doherty architectures are more or less well suited for various applications. For instance, architectures configured for high gain may be more desirable for certain base stations. The wide variety of applications leads to a large variance in Doherty amplifier architectures and configurations.